A reaction in which an alkylbenzene and carbon monoxide are reacted using hydrogen chloride-aluminum chloride or the like as a catalyst to produce an alkylbenzaldehyde is known as the Gattermann-Koch reaction. In this production, in order to separate the product and the catalyst after the completion of the reaction, usually, the reaction mixture is treated with water, and therefore the regeneration of the catalyst is very difficult. In addition, also when the catalyst used in the reaction is discarded, hydrolysis treatment is required, and therefore a problem is that a large amount of waste is generated, and the treatment cost increases.
As one of the types of the Gattermann-Koch reaction, a method of using hydrogen fluoride and boron trifluoride as catalysts is disclosed (see Patent Literature 1 and Patent Literature 2). In this type, substances having high vapor pressure, hydrogen fluoride and boron trifluoride, are used as catalysts, and therefore hydrolysis is not required for the separation of the product and the catalysts, and hydrogen fluoride and boron trifluoride can be circulated and reused, and this type is one of industrially very excellent aromatic aldehyde production methods. As a method for recovering hydrogen fluoride and boron trifluoride from an alkylbenzaldehyde-hydrogen fluoride-boron trifluoride complex solution that is a product of the Gattermann-Koch reaction in which hydrogen fluoride and boron trifluoride are used as catalysts, specifically, a method of thermally decomposing the complex solution under pressurization using benzene as a heat medium is disclosed (see Patent Literature 3).
Indene is one of aromatic compounds and is a compound useful as a raw material of various industrial chemical materials, perfumes, medicines, agricultural chemicals, optical functional materials, electronic functional materials, and the like.
Indene is generally obtained by distillation from coal tar fractions, and contains benzonitrile, phenols, pyridines, anilines, and the like as impurities. These impurities contained in indene cause side reactions in a reaction system and/or in the subsequent purification step and the like and cause a decrease in productivity and therefore are desirably removed. Among the above impurities, phenols, pyridines, and anilines can be removed by treatment with an alkali or an acid. On the other hand, benzonitrile is neutral, cannot be removed even by treatment with an acid or an alkali, and is difficult to completely separate even by precision distillation.
As a method for removing benzonitrile from indene, Patent Literature 4 discloses a method in which a solid alkali is added to tar-based light oil containing indene, the mixture is heat-treated at a temperature of 100° C. or more, and the precipitated insoluble matter is removed followed by distillation to recover indene.
In addition, Patent Literature 5 discloses a method in which a coal tar fraction comprising indene is catalytically reduced to obtain a mixture in which indene is converted into indan, and benzonitrile contained as an impurity is converted into amines such as benzylamine, dibenzylamine, and tribenzylamine, and this mixture is acid-washed to remove the amines contained in the mixture.